Cellulose-based films have an extensive history and technology. A common characteristic is that such films are produced by chemical, mechanical or combinations of chemical and mechanical processing of structural plant matter to provide a sheet-like matrix. This matrix contains dispersed or partially disintegrated cell walls and may contain numerous additives to improve processing or end-use function. The most prevalent commercial form is paper and paper related constructs such as cardboard or corrugated cardboard. Other specialized products are well known in the art such as tissue and glassine papers representing the extremes of mechanical processing. Tissues are low bulk density web like entanglements of dispersed plant fibers with low additive content, whereas glassine is a high density fragmented fiber product with substantial additive content. Many modifications of the above constituting commercial forms selected for specific function are known in the art of paper and paper related products.
Paper products and paper related constructs have been traditionally manufactured from rolled sheet stock. In the paper making process, a dispersed structural plant cell suspension is deposited on a mobile belt or static filtering interface such as a woven screen to provide a fiber entangled mat which is dewatered by mechanical or vacuum assisted expression and subsequent thermal assisted evaporation to provide a continuous or discrete sheet. These products are deliberately calendered or compressed to further enhance physical entanglement. This results in a higher tear modulus, better wet strength and hence less dispersibility, and smooth surfaces for high density roll production. While these properties are desirable for purposes such as packaging applications, they are diametrically opposed to those desired for the application intended in accordance with this invention. That is to say, conventional paper and paper related products are not considered as desired components of comestibles and have low organoleptic acceptance.
Fine paper products such as glassines and tobacco wrapper products, in contrast to packaging forms of cellulosic films, are produced by evaporative processing only. Typically a dispersed cellulosic phase is cast on a horizontal nonfiltering surface such as a belt and evaporative removal of the volatile continuous phase is effected as the belt moves into an elevated thermal environment. The resulting film is removed from the mobile support as a continuous sheet and collected in rolls for further processing and conversion into discrete forms for the intended use. As with conventional paper products the film/sheet is characterized by high wet strength, low dispersibility and desirably smooth surfaces on both sides. Again, these products have low organoleptic acceptance.
In contrast to paper related products, numerous film products based on natural polymers such as proteins, gums and starches are organoleptically well tolerated. Additionally, synthetic, water soluble polymers, such as those based on maleic anhydride, polyvinylpyrrolidone and cellulose ethers are also well accepted. However, films derived from water soluble polymers or hydrocolloids suffer from the very property that makes them organoleptically acceptable and easy to make, i.e. they readily disintegrate in the presence of water. With the exception of dried cereal products and powdered mixes, most food products contain substantial water.
Consequently, an edible film possessing the beneficial particulate structural characteristics of paper, yet displaying the organoleptic quality of water soluble polymer films would be useful in applications for improving processed food products. Such films could serve as lipophilic or hydrophilic barriers within a compartmentalized food construct, as edible wraps or packaging materials, as a texturizing and laminating agent or structural enhancement component. The application opportunities for such films are numerous and diverse. Yet in spite of need and opportunity, such films have not become commercially available. The physical constraints on the products produced by continuous cast film technology which are based on belt systems have limited the application of the resulting products in food systems.
Drum driers have been used as a means of continuous drying of high solids, viscous products. Water or the continuous solvent phase is removed by evaporative means through heat transferred to the external surface of the drum from steam delivered to the internal cavity of the drum. In contrast to dispersed droplet drying such as spray drying, very high viscosity materials can be processed efficiently. In usual practice the dried product is removed from the drum by a scraper assembly or doctor knife in the form of brittle flakes. Films are not desired as their release is generally a problem and uneven build up on the drum leads to poor control of heat transfer and ultimately unstable drying. Furthermore, all products dried on drum driers are destined to ultimately be recovered in powdered form and a substantially sheetlike released product is difficult to collect and grind. Hence drum driers have historically been used to produce products which are not discharged as flexible film sheets.